ZS250-5 Bike won't go over 60 mph?

[pjk]

I recently bought my first bike, it is a 2006 Zongshen ZS250-5 Sports bike. 250cc. It has around 1700 miles on it, and according to the previous owner, it had been sitting in a shed for about 6 months before I got it.

Anyways, it starts up fine. However, I just took it on the highway for the first time today, and couldn't get it over 60 mph. It goes up to 120 mph on the speedometer, and up to 14k rpms, but I couldn't get it over 8k rpms either. I have to get it all the way to 4th gear to go around 40, and then anything above is 5th gear. With full throttle in 5th, it goes around 7k rpm and 55-60 mph, and I can feel it cutting out a bit like it isn't getting gas.

So, my question is: how do I fix this? Is it just a cheap bike and I am SOL? What do you suggest I do? I think I will take it to a local cycle shop to see if I can get it tuned up and whatnot, but I'm wondering if there is anything I can do myself, as I'd like to learn.

Many thanks in advance! I greatly appreciate your time.

[FastDoc]

Yours runs, so you have other ZS250 owners beat.

This bike does not seem to share the exceptional reliability of the ZS200GY.

As far as performance goes I never got mine running so I have no first hand info, but I would expect a mildly tuned OHC 230cc (it's only nominally a 250) to go about 75 with a 180 pound or less sized person on it. This would mean level road with no wind and tucked. At least 70.

The speed and tach are generic and have nothing to do with any particular application. They do look good though.

Based on my personal experiance, I'd start by checking the compression. You should be getting at least 125 PSI, hopefully more than 150. Start there.

[katoranger]

Since it sat for awhile I would suspect the carb to possibly be plugged too.

A good carb clean may be needed.

[Weldangrind]

Welcome!

Most China bikes are a little on the lean side. A fatter main jet might be the answer, especially if the PO modified the intake or exhaust at all.

[xboxice]

Since it sat for awhile I would suspect the carb to possibly be plugged too.

A good carb clean may be needed.

This might be old post but this is whats needed drain carby and fuel tank of old fuel put new oil in and new fuel this should fix that issue straight away.

[Weldangrind]

Sometimes that's not adequate. I remove the carb, turn it upside down and remove the float bowl, remove the float valve, main jet and slow jet and blast all passages with aerosol carb cleaner. I carefully inspect the main and slow jets to see if they're plugged and clean/replace as necessary.